This invention relates generally to Digital Subscriber Line (DSL) technology, and more particularly to a method for gain estimation using ShowTime signals of analog amplifier deployed in the middle of the line and used to increase throughput of the DSL.
Discrete Multitone (DMT) modems has initialization process, which is composed of the following phases:                Handshake (HS)        Channel discovery        Training        Channel analysis and exchange        
When the initialization sequence is completed, data transmission (ShowTime) is initiated. An example of these steps is depicted in FIG. 1 (see ITU G.993.2 standard, figure 12-5).
Analog amplification can be used to increase the signal power of DSL to enable greater reach (coverage) and bandwidth. Analog amplifier magnifies the signal without terminating it. FIG. 2 is a schematic diagram presenting an analog amplifier along the telephone line, which connects between DSL Access Multiplexer (DSLAM) 10 and a Customer Premises Equipment (CPE) 12. D1 is the distance from the DSLAM 10 to the amplifier 14, and D2 is the distance from the amplifier 14 to the CPE 12.
As disclosed in U.S. Pat. No. 7,587,042, in order to be able to put the amplifier in a variety of locations along the line, the amplifier must have a configurable gain.
Using a wrong gain might result with line failing to activate or with non-optimal performance, either because the gain is too low, thus the signal arriving at the receiver is too weak, or because the gain is too high, thus the amplifier is saturated, and the signal is distorted.
U.S. Pat. No. 7,587,042 discloses a method for gain estimation based on the HS tones. This method suffers from several drawbacks, since the gain is not estimated on the actual signals that are transmitted over the line. For example:                The HS standard (ITU g.994.1) defines the maximal transmission level allowed during HS signaling. Some DSLAM/CPE transmit less than the maximal definition, resulting in an estimation error.        Some DSLAM/CPE transmit higher that the maximal allowed value (violating the standard). While this violation does not affect the normal activation of the modem, it results in an estimation error.        